Internally cooled valve for internal combustion engines, as well as method and device for the production thereof

ABSTRACT

A method and a device for the production of an internally cooled inlet or outlet valve for internal combustion engines, together with the resultant valve includes provision of a workpiece, which has a cylindrical stem and a cylindrical hole and, extends in the axial direction from one end of the valve stem. The method includes reshaping the end of the valve stern by form rolling of the cylindrical stem to a smaller diameter, wherein a diameter of the cylindrical hole is reduced, wherein the cylindrical hole remains. The method further includes reshaping by form rolling the section of the workpiece that is adjacent to the valve stem to form the valve head.

The present invention relates to cooled valves for internal combustionengines. More particularly, the present invention relates to asodium-cooled intake or exhaust valve for an internal combustion engine,and in particular to its method of production, and to a device for theproduction of the valve by a rolling process.

Internally cooled, or more particularly, sodium-cooled exhaust valveshave been of known art since 1935 at the latest.

Sodium cooling and its effects are well known in the prior art, and thetechnical advancements of recent years have mainly concerned anincreased volume of coolant in the area of the valve disk and simplifiedproduction processes, so as to be able to produce sodium-cooled valvesmore cost-effectively.

However, there continues to be a need for cost-effective and rapidproduction of internally cooled valves, as well as for an improvement ofthe cooling properties of existing intake and exhaust valves. A needalso exists to have available a cavity valve with maximum coolingperformance, which continues to function reliably even at the highestexhaust gas temperatures. It is further intended to reduce the number ofcomponents and joint lines of internally cooled valves for reasons ofrobustness and cost.

In accordance with the present invention, a method is provided for theproduction of an internally cooled intake or exhaust valve for internalcombustion engines, which, instead of being based on the metal-cuttingmethods of known art, is based on the reshaping of a workpiece, or asemi-finished product. The method comprises the provision of aworkpiece, which comprises a stem and a cylindrical hole, which extendsin the axial direction from one end of the valve stem. The valve stemend of the workpiece later forms the part that is located at the valvestem end of the finished valve. The valve stem end is reshaped by formrolling of the stem to a smaller diameter, wherein the diameter of thecylindrical hole is reduced, wherein the hole remains. The hole laterforms the cavity for a coolant that can move in the cavity in order totransfer heat from an uncooled valve disk in the direction of a cooledvalve stem. The method further comprises the reshaping by form rollingof a section of the workpiece that is adjacent to the valve stem to forma valve head. Here the valve head is also reshaped by form rolling. Inthis basic embodiment of the method at least the valve stem, with a borelocated therein, is rolled to a smaller diameter. The method can also beapplied to tubular workpieces so as to produce the stem and upper partof a valve disk, wherein a lower part of a valve disk can be formed by acover, which is bonded to the upper part of the valve disk.

In a basic embodiment the method is based on the reshaping of aworkpiece that comprises a cylindrical stem and a cylindrical holelocated therein, extending in the axial direction from one end of thevalve stem. The valve stem end is reshaped to a smaller diameter by formrolling of the cylindrical stem, wherein a diameter of the cylindricalhole is reduced, wherein the cylindrical hole remains, but can lose itscylindrical shape, since the workpiece is less strongly reshaped in thearea of the valve disk than in the area of the valve stem end. Theinitially cylindrical hole later forms the cavity for a coolant.

Throughout the text, the term “workpiece” is used in the meanings ofworkpiece and semi-finished product, in order to avoid any unnecessaryrepetition of the corresponding terms, and any unnecessary prolongationof the text. The terms “workplace” and “semi-finished product” are hereused synonymously.

The method comprises a reduction of the diameter of the stem and thebore located therein, together with a shaping of at least the rear faceof the valve disk by form rolling. In the basic embodiment of themethod, the nature of the formation of the valve disk face is not yetconsidered.

In an exemplary embodiment of the method, prior to form rolling, theworkpiece comprises a diameter that is at least equal to that of thevalve disk of the finished valve, and the method further comprises formrolling of a transition section between the valve head and the valvestem to form a concave fillet. By this means, the rear face of the valvedisk is produced by form rolling. It is also envisaged that the chamferfor the valve seat and/or the disk rim will be generated by formrolling.

In a further exemplary embodiment of the method, the workplace iscup-shaped. The cup-shaped workpiece has a diameter at the base of theworkpiece that corresponds at least to that of the valve disk. Thecylindrical hole is designed as a blind hole, which extends from one endof the valve stem in the direction of the base of the cup-shapedworkpiece, wherein the form rolling comprises a reshaping of the stemand a shaping of the valve head with at least the valve disk upper face.In this embodiment of the method, the chamfer of the valve seat and avalve edge are in particular also to be produced by form rolling. Thebase of the workpiece forms the valve disk face and can be brought intoits final shape already before the form rolling process. However, it isalso possible to provide a stub axle on the valve disk face in order tobe better able to guide the valve during the rolling process.

In a further exemplary embodiment of the method for the production of aninternally cooled valve for internal combustion engines, an outer basesurface of the workpiece already has the shape of the valve disk. With aworkpiece of this kind, only the rear face of the valve disk has to beprocessed by rolling and not the valve disk face.

In an additional exemplary embodiment of the method for the productionof an internally cooled valve for internal combustion engines, theworkpiece is cup-shaped and has a larger diameter at its base than inthe area of the cylindrical stem. By this means, a thinner stem can beused for the workpiece, which enables easier processing in the formrolling process. Here the stem does not have to be rolled from a valvedisk diameter to the valve stem diameter; instead a smaller amount ofreshaping can be sufficient in order to be able to produce the valvewith a cavity in the valve disk.

In a further exemplary embodiment of the method for the production of aninternally cooled valve for internal combustion engines, the workpieceis held between the rollers by guides. The guides can compriseindividual rollers that abut against an outer surface of the valve stemor valve disk. It is also envisaged that guides will be used, which arein sliding contact with an outer peripheral surface of the valve orworkpiece, and hold the valve or workpiece centrally between therollers. The rollers or sliders can be tracked so as to keep the axis ofthe valve or workpiece in the plane or surface that is spanned by thetwo axes of the rollers.

A further exemplary embodiment of the method for the production of aninternally cooled valve for internal combustion engines includes hotrolling of the workpiece.

The method can also include heating of the workplace by heaters, such asinduction heaters or gas burners, in order to enable a recrystallisationof the material of the workplace, and to counteract the effects ofstrain hardening.

In an additional exemplary embodiment of the method for the productionof an internally cooled valve for internal combustion engines, thelatter further comprises an axial movement of the workpiece in thedirection towards the stem end during the rolling process. In thismanner only a part of the stem can be rolled to a smaller diameter,which should reduce the mechanical load on the rollers and the rollingdevice considerably.

A further exemplary embodiment of the method for the production of aninternally cooled valve for internal combustion engines furthercomprises a rotation of the workpiece during the rolling process. Thisdoes not relate to a machining process on a lathe; instead the workpieceis driven during the rolling process. This step can be advantageous if,as a result of profile turning, sections with different radii makenecessary a variable slippage between the workpiece or valve and therollers. By means of a drive, or active rotation, of the workpiece,adjustments can be made as to which slippage arises on which diametersor radii, and which radii are rolled without slippage during the formrolling process.

Provision can also be to reduce the outer diameter of the stem byturning, after a desired inner diameter has been achieved by rolling. Inthis case the rolling process merely serves to achieve the innerdiameter of the cavity within the valve stem. Here the wall thickness ofthe material can be selected to be higher than the rolling process alonewould require.

The method is based on a basic embodiment involving the reshaping of aworkpiece that comprises a cylindrical stem and a cylindrical holelocated therein, extending in the axial direction from one end of thevalve stem. The valve stem end is reshaped to a smaller diameter by formrolling of the cylindrical stem, wherein a diameter of the cylindricalhole is reduced, wherein the hole remains, but can lose its cylindricalshape, since the workpiece is less strongly reshaped in the area of thevalve disk than in the area of the valve stem end. The initiallycylindrical hole later forms the cavity for a coolant. Here the cavityfor the coolant has a larger diameter in the area of the valve disk, asa result of which the heat transfer from the valve disk to the coolantcan be markedly improved.

In accordance with a further aspect of the present invention, a deviceis provided for the production of an internally cooled valve forinternal combustion engines from a workpiece, or semi-finished product.The device comprises a rolling mill for round cross rolling or forskewed rolling, wherein at least two rollers have the profile of anoutlet valve. Here the rollers comprise at least surfaces so as toreshape a stem and the rear face of a valve disk by form rolling. Thedevice for the production of an internally cooled valve thus comprisesforming rollers, which can roll a valve stem and the rear of the valvedisk from a workpiece. In particular, the rolling mill is designed forthe purpose of processing a hollow workpiece so as to produce a cavityin an internally cooled valve. Here the rolling mill is intended toreshape an essentially cylindrical hole or blind hole such that thelargest possible cavity of an internally cooled inlet or outlet valvecan be achieved. In one embodiment the device comprises only rollers,wherein additional guide rollers can be provided so as to guide theworkpiece between the rollers. Owing to the large difference in diameterbetween the valve stem and the valve disk diameter, it is not possibleto roll the valve with a rolling device that comprises three interactingrollers.

In an exemplary embodiment of the device for the production of aninternally cooled valve, the device further comprises a mandrel that canbe inserted into a hole of a workpiece, so as to guide the workpieceduring the rolling process. On the one hand, the mandrel can serve as aguide, and on the other hand can serve as a gauge so as to indicate whenan inner diameter of a rolled workpiece has achieved a prescribeddiameter.

In a further exemplary embodiment of the device for the production of aninternally cooled valve, the device further comprises at least one guideso as to hold and guide the workpiece between the rollers, wherein theat least one guide comprises a sliding element and/or one or a pluralityof rollers, which abut against an outer surface of the workpiece. Theseguides hold the stem and/or the disk between the rollers so as to beable to exert a maximum rolling force on the workpiece.

In a further exemplary embodiment of the device for the production of aninternally cooled valve, the at least one guide comprises a plurality ofrollers, at least one sliding element, which abuts against an outersurface of the workpiece, and/or a mandrel extending into the bore ofthe workpiece. In this manner, the workpiece can be assigned a definedinner diameter in the area of the stem. Furthermore, a mandrel that canbe lubricated or provided with a release agent can also be used for thepurpose of achieving a reduction in the thickness of the wall of thevalve stem, with an elongation of the valve stem. A polished mandrel canbe pulled out of the cavity after the rolling process. The mandrel canalso be tapered so as to facilitate extraction of the latter.

In an exemplary embodiment of the device for the production of aninternally cooled valve, the at least one guide comprises a slidingelement, or one or a plurality of rollers, that abut against an outersurface of the workpiece. The sliding element can be lubricated from anexternal source so as to reduce the friction and wear on the slidingelement. Furthermore, the plurality of rollers can be matched to thecontour of the valve so as to exert a uniform pressure on the workpieceduring the rolling process. The guides can be arranged on both sides ofthe workpiece, or only on one side. The individual rollers of the atleast one guide can also be arranged such that they can be displaced inthe axial direction so as to avoid the rollers rolling in on the stem.The sliding element can have a contour that corresponds to the negativeof the contour of the valve, so as to allow the most uniform possibletransmission of force onto the workpiece.

In another exemplary embodiment of the device for the production of aninternally cooled valve, the latter comprises at least one load cell onthe at least one guide, together with individually driven rollers, and acontroller that controls the rotational speed of the rollers such thatthe force on the guides is minimised. Here the workpiece is heldcentrally between the two rollers by means of a differential activationof the rollers, such that the load and the wear on the guides can beminimised. By means of an appropriate controller, the service life ofthe rolling device can also be increased, since the intervals at whichthe guides must be replaced can be extended.

In an additional exemplary embodiment of the device for the productionof an internally cooled valve, the at least one guide comprises aplurality of rollers, at least one sliding member, which in each caseabut against an outer surface of the workpiece, and/or a mandrelextending into the bore of the workpiece.

In a further exemplary embodiment of the device for the production of aninternally cooled valve, the axes of the rollers are arranged skewedrelative to one another at an angle of 1° to 12°, preferably of 2° to10°, and more preferably of 3° to 8°. This embodiment relates to askewed rolling method, in which the rollers are arranged separated at adistance from one another and not parallel to one another. Depending onthe rolling direction and the separation distance between the rollers, aworkpiece can be conveyed in the axial direction during the rollingprocess. This effect is particularly strongly pronounced if the (least)separation distance between the axes of the rollers is located near oneend of the rollers. In this configuration, it has not yet been definedhow the axis of the workpiece is aligned. It is possible to use an axisof the workpiece that runs parallel to an axis of the rollers. In thiscase, the workpiece is rolled adjacent to one roller, while the otherroller is either in contact with only part of the surface of theworkpiece, or has a surface that allows the whole surface to be rolledsimultaneously.

In another exemplary embodiment of the device for the production of aninternally cooled valve, the axis of the workpiece and the axes of eachof the rollers are arranged skewed relative to one another at an angleof 0.5° to 6°, preferably of 1° to 5°, and more preferably of 1.5° to4°. In this case the rolling device is a so-called skewed rollingdevice. In the case of skewed rolling, the roller axes are arrangedcrossed, or skewed, relative to one another. This generates alongitudinal feed in the workpiece as it rotates about its longitudinalaxis. The workpiece is held in the nip by means of support blades orguide rollers. The roller gauge can be configured such that the nipnarrows. Skewed rolling can also be carried out with correspondinglyshaped rollers, such that overall a nip is formed with a constantseparation distance. In the present case, however, the nip ideally hasthe contour of an intake or exhaust valve.

In an additional exemplary embodiment of the device for the productionof an internally cooled valve, at least one of the rollers, preferablyboth rollers, has a hyperboloidal, or rotationally hyperboloidal, outersurface. For lack of a more appropriate name the term hyperboloidal, orrotationally hyperboloidal, outer surface here relates to ahyperboloidal shape that is not formed from straight lines or sections,but from the profile lines of an inlet or outlet valve, in particular ofthe stem and the rear face of the valve disk. The term hyperboloid hererelates to a single-shell hyperboloid, which has the familiar waistedshape and forms circles sectioned, at right angles to the axis ofrotational symmetry. The degree of skew of the shapes that generate therotational hyperboloid is here intended to correspond exactly to therespective skew of the axes of the workpiece and the roller, since underthese conditions (in the case in which straight lines generate thehyperboloid), a cylindrical workpiece can be rolled. If thehyperboloidal roller is produced with the profiles of a valvestern/disk, waisted rollers ensue, which can generate a valve with astraight valve stem using the skewed rolling process. This embodimentrequires the greatest costs for the means of production, but at thepresent time can be expected to provide the best results.

In a further exemplary embodiment of the device for the production of aninternally cooled valve, the device further comprises an axial guide orclamping chuck so as to guide and/or hold the workpiece, starting fromthe disk face. With the axial guide the workpiece can be pressed againstthe rollers in the axial direction so as to be able to form the concavefillet of the rear face of the valve disk. In a basic embodiment theaxial guide just prevents the workpiece from moving axially out of therollers in the direction of the valve disk during the rolling process.If a clamping chuck is used, the workpiece must also have a shoulder, onwhich the clamping chuck can grip the workpiece. The axial guideprovides increased process assurance for the reshaping of the rear faceof the valve disk.

In an additional exemplary embodiment of the device for the productionof an internally cooled valve, the device further comprises an actuatorthat can move the workpiece axially away from the base in the directionof the valve stem end. The said actuator can act directly on theabove-cited axial guide or the clamping chuck. By means of the actuator,the valve stem can be slowly rolled from the end of the valve stem inthe direction of the valve disk, which can significantly reduce the loadon the rollers. It is also possible to monitor and execute moreprecisely the process of reshaping the rear face of the valve disk.

In another exemplary embodiment of the device for the production of aninternally cooled valve, the device further comprises a drive thatrotates the workpiece during rolling at a predetermined and possiblyvariable rotational speed. Due to the large difference in diameterbetween the valve stem and the valve disk, strong torsional forces ariseduring rolling, which can destroy the workpiece during the reshapingprocess. It can therefore be necessary, during the profile turning ofsections with different radii, to ensure a variable slippage between theworkpiece or valve and the rollers. This can be achieved here by drivingor actively rotating the workpiece, in particular the valve disk, inorder to keep the torsional forces of the workpiece as low as possible,in particular at the transition section between valve disk and valvestem. The rolling device can also be provided with lubrication so as tomaintain wear of the rollers as low as possible in sections in whichslippage is present.

In another exemplary embodiment of the device for the production of aninternally cooled valve, the device further comprises a heating elementso as to heat the workpiece during the rolling process. Thus, arelatively small workpiece can be hot rolled even with relatively largerollers, without the need to fear too severe a cooling of the workpieceduring the rolling process.

In addition, during the reshaping further energy can be introduced intothe workpiece by means of inductive or autogenous heating, or gasheating.

The invention relates to a method in which, starting from a tubular orcup-shaped workpiece, a hollow valve head section and a hollow valvestem are generated by hot rolling. The valve that is generated can beproduced without any joint lines, if the starting point is a cup-shapedworkpiece. The valve that is generated can have an enlarged cavity inthe area of the valve disk, so as to accommodate an increased volume ofsodium in the valve as the coolant. A special feature comprises thereshaping by two rollers and a guide, wherein at least one roller isarranged at an angle relative to the workpiece axis and the second axis.Here each of the rollers also has, at the end face facing the workpieceaxis, a negative shape or concave geometry of the valve head blank.

Both rollers are able to move towards each other during reshaping,wherein one roller can also be rigidly held in position and only theother roller (and the workpiece) can be moved. Here the workpiece duringthe reshaping process can rest on a base or guide, and is pressed by themovement of the rollers against the guide and thereby rotated. Inaddition, the workpiece can also be moved axially against the rollers,wherein the negative shape on the end faces of the rollers forms theconcave geometry of the valve head blank. Here the position of a centralaxis of the workpiece can be located below the central axes of therollers. So as to reduce the friction on the workpiece, the guide can bemounted on rollers.

In another exemplary embodiment of the device for the production of aninternally cooled valve, at least one of the rollers has a surfacestructure that causes transport of the material of the workpiece in theaxial direction. In this embodiment, a fine thread pattern or anotherroughened surface structure is applied onto at least one surface of oneof the rollers. The thread pattern or other roughened surface structurecan or should be primarily located on the inclined axis. Here therollers can be produced from a metal alloy or a ceramic compositematerial, or in each case can comprise the latter.

By virtue of the angle of the roller(s) relative to the workpiece, andthe thread pattern or other roughened surface structure on at least oneof the rollers, a central tensile force is exerted on the workpiece, asa result of which an elongation of the blank can be achieved in additionto the diameter reduction.

In accordance with a further aspect of the present invention, aninternally cooled valve for internal combustion engines is provided thathas been reshaped and produced with one of the methods as describedabove, or with the device as described above. The valve is characterisedin that, before reshaping, the workpiece comprises a stem and also acylindrical hole that runs from one end of the valve stem in the axialdirection. At least the stem of the valve has thereby been reshaped byform rolling of the stem to a smaller diameter, wherein the hole hasbeen maintained and wherein the workpiece before the form rollingprocess comprises a diameter of at least that of the later valve disk,and wherein a valve head with a concave fillet is produced by formrolling,

In a basic embodiment the valve is reshaped from a workpiece thatcomprises a cylindrical stem and a cylindrical hole located therein,which extends from one end of the valve stem in the axial direction. Thevalve stem end has been reshaped to a smaller diameter by form rollingof the cylindrical stem, wherein a diameter of the cylindrical hole isreduced, wherein the cylindrical hole remains as a hole, but can loseits cylindrical shape, since the workpiece is less strongly reshaped inthe area of the valve disk than in the area of the valve stem end. Theinitially cylindrical hole later forms the cavity for a coolant. Withnon-uniform reshaping, it is thus possible to produce a cavity with alarger diameter, and thus a larger surface area, in the area of thevalve disk, which significantly improves the heat transfer between thevalve disk and the coolant.

The valve is thus an internally cooled valve, and the stem and at leastthe rear face of the valve disk have been at least partially produced bythe reshaping process. Here further machining process steps can followin order to achieve the desired surface properties of the stem and/orthe rear face of the valve disk. In a basic embodiment, the valve canalso be reshaped from a tubular workpiece, wherein an opening on thevalve disk can later be closed by means of a cover.

In another exemplary embodiment of the internally cooled valve, theworkpiece is cup-shaped, wherein the cup-shaped workpiece has a diameterat a base of the workpiece that corresponds at least to that of thevalve disk, wherein the cylindrical hole is a blind hole that extendsfrom one end of the valve stem in the direction of the base of thecup-shaped workpiece. In this embodiment, a larger cavity can begenerated in the area of the valve disk than was previously possiblewith a one-piece valve.

In a further exemplary embodiment of the internally cooled valve forinternal combustion engines, the workpiece is cup-shaped and thecup-shaped workpiece has a larger diameter at its base than in the areaof the cylindrical stem. Here it is intended that the inner diameter ofthe blind hole should essentially determine the diameter of the cavityin the area of the valve disk. By virtue of the smaller diameter of thecylindrical stem, the reshaping work and thus the residence time of theworkpiece in the rolling device can be reduced. Furthermore, the wallthickness of the cylindrical stem can be increased, which in turn willhave a positive effect on the reshaping process.

In a further exemplary embodiment of the internally cooled valve, afterthe reshaping process the cylindrical hole forms a cavity that extendswithin the valve stem and the valve disk, and which is partially filledwith sodium and sealed.

In yet another exemplary embodiment of the internally cooled valve, thishas been produced from a workpiece with a non-cylindrical stem with anouter contour and a cylindrical hole. By a reshaping process of thevalve stem end by means of form rolling to form an essentiallycylindrical valve stem, the outer contour is transferred at least inpart to the non-cylindrical hole after the reshaping process. After thereshaping process the non-cylindrical hole has an inner contour thatcorresponds to the outer contour. This can be achieved with or withoutan elongation of the stem, during the rolling process. The dimensions ofthe outer contour that are required in order to achieve a desired innercontour can be determined relatively easily by means of experiments.

In what follows the present invention will be explained by way ofillustrations of exemplary embodiments. The figures represent purelyschematic illustrations.

FIGS. 1A to 1D illustrate an embodiment of an inventive device for theproduction of an internally cooled valve from a tubular workpiece, andthe associated production method.

FIGS. 2A to 2C show a further embodiment of an inventive device for theproduction of an internally cooled valve from a cup-shaped workpiece,and the associated method.

FIGS. 3A to 3C illustrate a further embodiment of an inventive devicefor the production of an internally cooled valve from a short cup-shapedworkpiece, and the associated method.

FIGS. 4A to 4B show an additional embodiment of an inventive device forthe production of an internally cooled valve from a short cup-shapedworkpiece by means of skewed rolling.

FIGS. 5A and 5B illustrate a further additional embodiment of aninventive device for the production of an internally cooled valve from ashort cup-shaped workpiece, and the associated method.

FIGS. 6A and 6B illustrate a further additional embodiment of aworkpiece and an internally cooled valve

In both the description and the figures, the same or similar referencesymbols are used to refer to the same or similar components andelements. In order to avoid a description of unnecessary length,elements that have already been described in one figure are notseparately mentioned in further figures.

In order not to make the drawings unnecessarily complicated, the partsof the rolling device that serve to carry, mount, or drive the rollers,or to move them at right angles to a roller axis, or in the direction ofa workpiece axis, have not been illustrated. Any mountings orsuspensions of guides and axial guides have also been omitted from theillustrations.

FIG. 1A shows an inventive rolling device with two forming rollers 42.The forming rollers are provided with stub axles 64, with which they canbe accommodated in a housing of a rolling device. The forming rollers 42can also be driven together or individually via the stub axles.

At the top of FIG. 1A, the axes are shown in a plan view, wherein theplane of the drawing extends essentially through the axes 48 of therollers 42, and the axis 46 of the workpiece 14. The outer contour ofthe forming rollers 42 corresponds to the negative profile of an inletor outlet valve that is to be rolled. Between the forming rollers 42 isarranged a tubular workpiece 14 with a through-opening or through-hole28. The axis 46 of the workpiece 14 and the axes 46 of the rollers 42are aligned in parallel. At the bottom of FIG. 1A the rollers 42 and theworkpiece 14 are shown in a view in the axial direction. In FIGS. 1A and1B the rollers are designed for a round cross rolling process. Therollers are designed as forming rollers 42. The respective directions ofrotation of the rollers and the workpiece are indicated by the arrows60. In round cross rolling, the workpiece 14 rotates about the axis 46of the workpiece 14 in the opposite direction to the forming rollers 42between two forming rollers rotating in the same direction. By theinfeed of at least one tool, that is to say, one forming roller 42, thework piece 14 is reshaped. Here it is shown that both rollers are movedtowards the workpiece 14 in the direction of movement and forceapplication 62. However, it is also possible to move just one of therollers 42 in the direction of the workpiece 14, i.e. to move it towardsthe other roller, wherein the axis of rotation of the workpiece 14 isdisplaced. Here the workpiece 14 is held in the axial direction by aclamping chuck 56, whose clamping jaws are shown. Here the clampingchuck 56 serves as an axial guide 54 so as to prevent the workpiece 14from moving during the rolling process in the direction of what willlater be the valve disk; such movement is brought about by the axialcomponent of the rolling forces in the area of the rear face of thevalve disk.

The form rolling process has, inter alia, the advantage that themolecular chain structure in the workpiece 14 is retained, whichgenerates an undisturbed orientation of the fibres. As a result it canalso be established on the basis of the crystal structure usingmetallurgical methods on the finished valve as to whether it has beenproduced, that is to say, formed, by forming rollers.

The axes 48 of the forming rollers 42 define a plane, and while the axisof the workpiece 14 lies parallel to this plane, it is not in thisplane; instead in the drawing it is below this plane. In a rollingprocess, the workpiece 14 would be pushed downwards as soon as theforming rollers 42 initiate the rolling process. The workpiece 14 istherefore supported in the figure from below by a guide, moreparticularly, a radial guide 52, which serves as a radial guide. From anapplication of the force parallelogram it becomes clear that the forceacting on the guide can be much lower than the rolling forces that ariseas the forming rollers 42 move towards one another. A sliding frictioncan therefore be generated in the area of the support, even if strongrolling forces are generated by the rollers in the movement/rollingpressure direction.

It is also possible to lubricate the surface of the radial guide 52 soas to reduce the wear of the contact surface with the radial guide 52.During the rolling process, the guide can be tracked upward in thedirection of the axis 46 of the workpiece 14, so as to reduce the loadon the radial guide 52. It is also envisaged chat a multi-part guide canbe used, which can adapt to the various stages of the reshaping process,in particular in the area of the valve head. It is also envisaged thatinstead of a rigid guide, a series of rollers can be used, which can beoperated with less wear. The rollers can be moved in the axial directionin order to avoid local deformation of the workpiece by the guiderollers.

Above the workpiece, a heating element can be mounted opposite theradial guide 52, which heats the workpiece 14 by flame, radiation orinduction, so as to ensure that hot rolling occurs throughout the wholeof the reshaping process.

In the rolling method used, the workpiece 14, before the rolling processin the axial direction, can be displaced upwards until it is flush withthe upper edge of the forming rollers. However, it is also possible tomove the workpiece 14 upwards in the direction of the valve stem endduring the rolling process, until the valve stem end is flush with theupper edge of the forming rollers.

Provision can also be made to drive the workpiece 14 by means of theclamping chuck, so as to achieve a slippage between the forming rollers42 and the workpiece 14, in particular in the area of the valve disk,more particularly, the rear face of the valve disk. Since the rear faceof the valve disk has a smaller surface area than the outer surface areaof the valve stem, it seems advisable to generate a slippage between therear face of the valve disk and the corresponding sections of theforming rollers 42, since otherwise the valve could be destroyed as aresult of the torsional forces between the rear face of the valve diskand the valve stem. The angular velocity ratios between stem and valvedisk are here at least as large as the corresponding radii ratiosbetween valve stem and valve disk. With a ratio of the valve disk tovalve stem diameter of about 5, in each case a ratio of the angularvelocities for the average diameter of the valve disk to the stemdiameter of about 2.5 ensues, which in a normal rolling process would besufficient to turn or tear off the valve disk from the stem. Therefore,provision can be made to drive the workpiece 14 during form rolling at ahigher speed in order to produce a slippage in the area of the valvedisk, which significantly offloads the transition section from the valvedisk to the valve stem and can thus prevent destruction of the workpiece14 during form rolling. For this purpose the clamping chuck can set intorotation by a separate drive, not shown, if the latter is provided.

Furthermore, the rolling device can be provided with a single-rollerrotational speed control, which is shown in detail in FIG. 1B, so as toreduce the wear on the radial guide 52. This is shown in detail in FIG.1B. In order not to make FIG. 1A too confusing, the controller is notshown in the latter.

FIG. 1B shows the same elements as FIG. 1A, namely the forming rollers42 and a finished form-rolled workpiece 14A, wherein the forming rollers42 are shown in a position at the end of the rolling process. Thedepiction is purely schematic. The forming rollers 42 have reshaped theworkpiece 14 into a reshaped workpiece 14A. The reshaped workpiece 14Astill has a through-hole 28, which extends through the whole of thevalve stem.

The form rolling device of FIG. 1B is provided with a load cell 66 forat least one radial guide 52, so as to measure the force with which theworkpiece is pressed by the forming rollers 42 against the radial guide52. The form rolling device of FIG. 1B is also provided withindividually driven forming rollers 42 which can be activatedindividually at a selected rotational speed. The load cell or forcesensor 66 is connected to a controller 68, which controls at least therotational speed, that is to say, the drive, of one of the formingrollers 42, so as to limit the force that the workpiece 14/14A exerts onthe radial guide 52 during the rolling process. Provision can also bemade for the controller to control a rotational speed, moreparticularly, that of the workpiece, in order to reduce or at leastlimit the load on the radial guide 52.

Here the workpiece is held centrally between the two rollers by means ofa differential activation of the forming rollers, or in anotherposition, such that the load and the wear on the guides 52 can beminimised. The system can also be used in the case of rolling deviceswith two guides. By means of an appropriate controller, the service lifeof the rolling device can also be increased, since the intervals atwhich the guides must be replaced can be extended.

Although the controller for limiting the load on the radial guide 52 isdescribed only in conjunction with FIG. 1B, it is explicitly emphasisedhere that the said controller should also be regarded as disclosed inthe case of the other embodiments that are shown in the figures. Thecontroller has been described only in FIG. 1B, as redundant repetitionwould only have increased the length of the description unnecessarily.

FIG. 1C shows the finished reshaped workpiece 14A, which comprises apart that essentially forms a valve body. The valve body has a valvestem 8, which at a lower end runs out into a valve disk 6, moreparticularly, the rear face 24 of a valve disk. The valve body does notyet comprise a valve disk face. The upper part of the valve stem 8terminates in the stern end 36, with which the valve can later beactivated. As illustrated, the stem end can be produced in the course ofthe form rolling process; however, it is also possible to shape the stemend 36 at a later stage.

The through-hole 28 has been reshaped into the cavity 10 in the valvedisk 6 and the valve stem 8. It is also possible to produce just thecavity 10 by reshaping and later to bring the valve stem to a finaldiameter by a machining process, should it not be possible to achievethe parameters of the diameter of the through-hole 28, or blind hole,and the wall thickness of the workpiece, before and after the formrolling process.

The workpiece can be separated from the tubular remnant along the dottedline that forms the separation line 30. On the valve disk face there isstill an opening 18, which can be closed at a later stage with a coverso as to form a finished valve.

FIG. 1D shows the finished valve 4 produced by means of reshaping. Thevalve body has a valve stem 8, which at a lower end runs out into avalve disk 6, more particularly, the rear face 24 of a valve disk. Theopening 18 on the valve disk face 22 is closed by a cover 20, which hasbeen bonded to the valve by friction welding, resistance welding,electron beam welding, or laser welding on a joint line 32.

The cavity 10 is filled with a sodium coolant 12. The coolant used isusually sodium, which is in a liquid state at the operating temperaturesof the internal combustion engine. Usually it is not the entire cavity10, but only ¼, ⅓, ½, ⅔ to ¾ of the cavity of the valve that is filledwith sodium. In operation, the sodium in the valve stem 8, that is tosay, in the cavity 10 of the valve stem 8, moves up and down and therebytransports heat from the valve disk 6 in the direction of the cooledvalve stem S (shaker cooling). The sodium moves within the valve 2during each opening and closing operation. The cavity 10 has beenproduced in the valve 2 in that the valve disk 6 has been provided onthe valve disk face 22 with an opening 18.

FIG. 2A corresponds essentially to FIG. 1A. A description of referencesymbols and elements that have already been described in connection withFIG. 1A will not be repeated here. Instead of a tubular workpiece 14, acup-shaped workpiece 16 is now used, in which a base already forms thevalve disk 6, that is to say, the valve disk face 22. Instead of athrough-hole a blind hole 26 is used.

The diameter of the workpiece 16 is larger in the area of what is laterthe valve disk than in the area of what is later the valve stem 8. Theworkpiece already has, either essentially or precisely, the height ofthe later valve. Here the valve stem is formed essentially by formrolling. The valve disk can already be shaped to a large extent by amachining process. The cup-shaped workpiece 16 is held in the axialdirection by an axial guide 54 so as to be able to form the rear face ofthe valve disk. Provision is also made to provide the cup-shapedworkpiece 16 with a shoulder on which a clamping chuck can engage, so asto be able to rotate the cup-shaped workpiece during form rolling at aspeed that can be selected. This was already explained in thedescription of FIGS. 1A and 1B. With a shoulder that is held in aclamping chuck, a slippage between the valve disk and the formingrollers can be achieved. The shoulder can be removed after the formrolling by a machining process.

In contrast to the embodiment of FIG. 1A, the wall thickness of thatpart of the cup-shaped workpiece 16, which later forms the valve stem,can be made thinner, which at a later stage results in a smaller wallthickness for the valve stem. Furthermore, in this design, thecup-shaped workpiece 15 is less strongly reshaped than the workpiece ofFIGS. 1A/1B.

In FIG. 2B, the valve is already finished to a large extent after theform rolling. The cavity 10 has a large diameter in the area of thevalve disk, which can be expected to result in improved coolingproperties. The stem has a smaller wall thickness than in the case ofFIG. 1B. By virtue of the lower degree of reshaping it is possible toroll the stem without it becoming necessary to reduce the outer diameterof the valve stem in a further machining process step.

FIG. 2C illustrates an internally cooled valve 4 in accordance with theinvention, which has a valve stem that terminates at its lower end in avalve disk. The upper part of the valve stem 8 terminates in a stem end36. Internally the valve is provided with a cavity 10, which is filledwith a coolant 12. The cavity can, for example, be filled with thecoolant through an opening or bore in the valve stem. In the area of thevalve disk the inventive valve has a cavity with a large diameter, whichcan exceed the diameter of the valve stem. Here the valve disk, with thevalve disk face 22, the rear of the valve disk 24, and the valve stem,are formed from one piece. The finished valve therefore has no jointlines, either in the area of the valve disk or in the area of the lowervalve stem. It is possible to close the cavity 10 by means of a valvestem end attached, for example, by means of friction welding, after ithas been filled with coolant.

FIG. 3A illustrates essentially the form rolling device of FIG. 2A. Adescription of reference symbols and elements that have already beendescribed in connection with FIGS. 1A or 2A will not be repeated here.In contrast to the forming rollers of FIG. 2A, the forming rollers ofFIGS. 3A are provided with a surface structure 58, which, during theforming rolling process, causes a transport of the workpiece material inthe axial direction. The surface structure 58, which causes a transportof the workpiece material in the axial direction, is designed here as athread pattern, which, with the rotation of the forming rollers 42,generates an axial force in the direction of what is later a valve stemend. With the surface structure, it is possible to use a shortercup-shaped workpiece 16. In the form rolling process, a force is alsoexerted in the axial direction onto the cup-shaped workpiece, as aresult of which the material during the rolling process can spread notonly in the radial direction but also in the axial direction.

Here the surface structure 58 is embodied as a thread pattern. Thethread pattern is designed with a small flank height and a small pitch,which only exerts forces, and does not roll a screw thread into thevalve stem.

When the forming rollers exert a pressure on the cup-shaped workpiece16, the material can flow not only in the circumferential and radialdirections, but also, as a result of the axial forces, is able to flow,that is to say, to deform, in the axial direction. In overall terms thiseffect results in an ability to start with a cup-shaped workpiece with alarger wall thickness, which can significantly increase the processreliability of the method.

It is, of course, also possible to provide only one of the formingrollers with the surface structure 58, which causes transport of theworkpiece material in the axial direction, or generates an axial forcein the workpiece.

FIG. 3B illustrates the rolling process for the cup-shaped workpiece 16in the direction of the valve stem end, wherein the materialdisplacement is indicated by thin arrows.

FIGS. 3A and 3B can operate without an axial guide if the surfacestructure 58 generates a sufficiently large axial force to deform therear of the valve disk face 24 by form rolling.

FIG. 3C shows a valve 4 that has been produced with the form rollingdevice of FIGS. 3A and 3B. It differs from the valve of FIG. 2C only interms of the crystal structure of the material.

FIG. 4A corresponds essentially to FIGS. 1A to 3A. A description ofreference symbols and elements that have already been described inconnection with FIGS. 1A to 3A will not be repeated here.

FIG. 4A utilises the same short cup-shaped workpiece 16 as is shown inFIGS. 3A and 3B. Instead of cylindrical rollers, the axes of which arealigned parallel to one another, the embodiment of FIG. 4A and FIG. 4Buses hyperboloidal forming rollers 44, whose axes are skewed relative toone another. The rolling method represents an skewed rolling method,because the axis of at least one of the forming rollers is inclined withrespect to the axis of the cup-shaped workpiece. Technically, the axesof the rollers are skewed relative to one another, wherein an anglebetween the axes can be specified as the angle in an orthogonalprojection of the axes. Here the axes 48 of the forming rollers are eachinclined at the same angle to the axis 46 of the cup-shaped workpiece16. As a result of the inclination and rotation an axial force isgenerated in the direction of what is later the valve stem end duringthe rolling process. Thus a similar effect, can be produced as with thesurface structure 58 in FIGS. 3A and 3B. It is also possible, of course,to equip the forming rollers of FIGS. 4A and 4B with an appropriatesurface structure 58, such as was disclosed in FIGS. 3A and 3B. Theforming rollers 44 form single-shell rotational hyperboloids, whosegenerators are not straight lines, but the profile of an inlet or outletvalve. Cylindrical rollers would not produce a cylindrical product, butrather a single-shell hyperboloid, since the separation distance betweenthe axes of the rollers increases with the distance from the smallestseparation distance. To compensate for this effect, the rollersthemselves must have the shape of a single-shell hyperboloid. In skewedform rolling the rollers must also have the profiling of the finalproduct, and thus form profiled single-shell hyperboloidal surfaces.

In contrast to the embodiments of FIGS. 1A to 3B, the workpiece is hereguided by two opposing radial guides 52, which guide the cup-shapedworkpiece 16 between the hyperboloidal skewed rollers 44. The guidesmust also be tracked during the form rolling process. Here it is also inparticular possible to use the single-roller controller of FIG. 4B inthe rolling device of FIGS. 4A and 4B.

The workpiece can be guided by an axial guide 54, but can also be held,guided and/or rotated, by a clamping chuck via a shoulder.

As in FIG. 1B, both radial guides 52 can each be provided with at leastone load cell 66, each of which is connected to a controller 68, whichin turn controls the rotational speed, that is to say, the drive, of atleast one of the forming rollers 44. Here again, the controller can beused for the purpose of holding the workpiece 16 accurately between therollers 44 and/or reducing the wear on the radial guides 52.

FIG. 4A illustrates the hyperboloidal forming rollers 44 in a finalposition after the form rolling process. When using hyperbolic formingrollers, torsional forces are generated in the stem, which are smallerat lower roller axis angles.

The larger the angle between the roller axes 48, the greater is theaxial force generated.

The embodiment of FIGS. 4A and 5B can also operate without an axialguide, since a sufficiently large axial force is generated by the skewedrollers. It is also possible to deploy the surface structure 58 of FIGS.3A and 3B in order to increase further the axial force generated duringthe rolling process.

FIG. 5A illustrates a combination of FIGS. 1A, 2A, 3A and 4A. As in FIG.1A, the cup-shaped workpiece is only guided from one side by means of aradial guide 52. The left-hand forming roller 42 has the same shape asin FIGS. 1A and 2A, and the axis of the left-hand forming roller 42 isaligned parallel with the axis of the cup-shaped workpiece 16. Theleft-hand forming roller is designed as a hyperbolic forming roller 44,as in FIG. 4A. The hyperbolic forming roller 44 is also provided withthe surface structure 58 of FIGS. 3A and 3B. The axis 50 of thehyperbolic forming roller 44 is inclined relative to the axis 48 of theleft-hand forming roller 42 and the axis 46 of the cup-shaped workpiece.Thus, during the form rolling process the right-hand hyperbolic formingroller 44 generates a strong axial force in the direction of what islater the valve stem end. With a suitable design this axial force issufficient to elongate a short cup-shaped workpiece 16 in the axialdirection during the form rolling process.

FIG. 5B illustrates the rolling device at the end of the rollingprocess. In FIG. 5B the hyperboloidal forming rollers 44 are located ina final position after the form rolling process. As a result of theshape of the rollers, the left-hand hyperbolic forming roller 44 coversthe upper valve stem end of the rolled valve. The shape of the rollersalso causes the valve disk to cover the lower part of the left-handhyperbolic forming roller 44. Likewise the right-hand hyperbolic formingroller 44 partially covers the valve disk of the reshaped workpiece 16A.The valve stem end covers the upper part of the line of contact of theright-hand hyperbolic forming roller 44 with the valve stem end.

With the one-sided guidance by the radial guide 52, the possibilityarises of installing a heater opposite the radial guide 52, which heatsthe cup-shaped workpiece by way of, for example, an induction heater ora gas heater, so as to hold the workpiece 16 within a temperature rangein which hot rolling, more particularly, hot skewed form rolling, ispossible.

FIGS. 6A and 6B illustrate a further additional embodiment of aworkpiece and an internally cooled valve. The workpiece that is shown inFIG. 6A corresponds essentially to the workpiece of FIG. 2A. In contrastto the workpiece of FIG. 2A the workpiece of FIG. 6A is provided with anouter contour 70. As in FIG. 2A, the blind hole 26 is designed as acylindrical hole. The outer contour 70 together with the cylindricalblind hole 26 produces a thickness variation of the stem.

As a result of the reshaping process the outer surface of the stem isreshaped so as to be essentially cylindrical. Here the outer contour 70is flattened and transferred inwards to the inner face of the blind hole26, wherein an inner contour is formed internally in the blind hole. Thethickness variation of the stem is essentially maintained, wherein thecontour after the reshaping process is now formed on the inner face,i.e. in the cavity 10, as an inner contour 72. Here the inner contour isdesigned such that it forms a Laval nozzle at the transition sectionbetween the valve disk 6 and the valve stem 8. It should be understoodthat other inner contours can be generated using this method. It shouldlikewise be understood that this principle can also be applied to theembodiments in which an elongation of the shank is also achieved duringthe reshaping process, as for example in FIGS. 3, 4 and 5. A to Crespectively. At the same time just a broadening and flattening of thecontour in the axial direction must also be considered. By this methodit is easily possible to achieve shaped cavities 10 with good flowcharacteristics, which allow a conical transition between the stem andthe valve disk. It can also be desirable to generate nozzle shapes, suchas the Laval nozzle illustrated in the cavity 10. With this method, itis possible using very simple technical measures to generate almost anysmooth or continuous inner contours 70.

It should be noted that all combinations of features of FIGS. 1A and 1B,to 5A and 5B, should also be considered as disclosed, inasmuch as theycan be technically implemented. This relates in particular to thecontrol or regulation of the individual roller speeds as a function offorces that have been measured on at least one radial guide.Furthermore, configurations are planned with one-sided and two-sidedsupport by means of radial guides for all embodiments.

REFERENCE LIST

-   4 Inventive internally cooled valve-   6 Valve disk-   8 Valve stem-   10 Cavity-   12 Coolant-   14 Tubular workpiece-   14A Reshaped tubular workpiece-   16 Cup-shaped workpiece-   16A Reshaped cup-shaped workpiece-   18 Opening-   20 Cover-   22 Valve disk face-   24 Rear of the valve disk-   26 Blind hole-   28 Through-hole-   30 Separation line-   32 Joint line-   36 Stem end-   42 Forming roller-   44 Hyperbolic forming roller-   46 Workpiece axis-   48 Forming roller axis-   50 Hyperbolic forming roller axis-   52 Guide/radial guide-   54 Axial guide-   56 Clamping chuck-   58 Surface structure that causes a transport of the workpiece    material in the axial direction-   60 Direction of rotation-   62 Direction of movement/roller pressure-   64 Stub axle-   66 Load cell-   68 Control of the forming rollers rotational speeds-   70 Outer contour-   72 Inner contour

1. A method for the production of an internally cooled valve (4) forinternal combustion engines, comprising: provision of a workpiece (14,16), which comprises a stem and a cylindrical hole (26, 28), whichextends from one end of the valve stem (36) in the axial direction,reshaping of the valve stem end (36) by form rolling of the stem to asmaller diameter, wherein a diameter of the cylindrical hole is reduced,wherein the hole (26, 28) remains, and reshaping by form rolling of asection of the workpiece (14, 16) that is adjacent to the valve stem (8)to form the valve head.
 2. The method for the production of aninternally cooled valve (4) for internal combustion engines, inaccordance with claim 1, wherein prior to the form rolling process theworkpiece (14, 16) comprises a diameter of at least that of the valvedisk (6) of the finished valve, and further comprising: form rolling ofa transition section between the valve head and the valve stem (8) toform a concave fillet.
 3. The method for the production of an internallycooled valve (4) for internal combustion engines, in accordance withclaim 1 or 2, wherein the workpiece (16) is cup-shaped, wherein thecup-shaped workpiece (14, 16) has a diameter at a base of the workpiece(16) that corresponds at least to that of the valve disk (6), whereinthe cylindrical hole is a blind hole (26), which extends from one end ofthe valve stem (36) in the direction of the base of the cup-shapedworkpiece (16), and wherein the form rolling process comprises areshaping of the stem and a shaping of the valve body.
 4. The method forthe production of an internally cooled valve (4) for internal combustionengines, in accordance with claim 3, wherein an outer surface of thebase of the workpiece (16) already has the shape of the valve disk (6).5. The method for the production of an internally cooled valve (4) forinternal combustion engines, in accordance with claim 3 or 4, whereinthe workpiece (16) is cup-shaped, and wherein the cup-shaped workpiece(16) has a larger diameter at a base of the workpiece (16) than in thearea of the cylindrical stem.
 6. The method for the production of aninternally cooled valve (4) for internal combustion engines, inaccordance with one of the preceding claims, wherein the workpiece (14,16) is held between the rollers by means of guides.
 7. The method forthe production of an internally cooled valve (4) for internal combustionengines, in accordance with one of the preceding claims, wherein theworkpiece (14, 16) is hot rolled.
 8. The method for the production of aninternally cooled valve (4) for internal combustion engines, inaccordance with one of the preceding claims, further comprising: axialmovement of the workpiece (14, 16) in the direction of the stem end (36)during the rolling process.
 9. The method for the production of aninternally cooled valve (4) for internal combustion engines, inaccordance with one of the preceding claims, further comprising:rotation of the workpiece (14, 16) during the rolling process.
 10. Themethod for the production of an internally cooled valve (4) for internalcombustion engines, in accordance with one of the preceding claims,further comprising: turning of the valve stem (8) to a desired outerdiameter, after a desired inner diameter of the valve stem (8) has beenachieved by rolling.
 11. The method for the production of an internallycooled valve (4) for internal combustion engines, in accordance with oneof the preceding claims, wherein the provision of the workpiece (14, 16)comprises a provision of the workpiece (14, 16) with a non-cylindricalstem with an outer contour (70) and the cylindrical hole (26, 28),wherein the reshaping of the valve stem end (36) by form rollingcomprises a reshaping of the valve stem end (36) by form rolling of thestem to a smaller diameter, wherein a diameter of the cylindrical holeis reduced, and a non-cylindrical hole with an inner contour (72)remains.
 12. A device for the production of an internally cooled valve(4) for internal combustion engines, from a workpiece (14, 16),comprising: a rolling mill for purposes of round cross rolling or skewedrolling, wherein at least two forming rollers (42, 44) have a profile ofan outlet valve.
 13. The device for the production of an internallycooled valve (4) in accordance with claim 12, further comprising: amandrel, which can be inserted into a hole (26, 28) of a workpiece (14,16) so as to guide the workpiece (14, 16) during the rolling process.14. The device for the production of an internally cooled valve (4) inaccordance with claim 12, further comprising: at least one guide so asto hold and guide the workpiece (14, 16) between the rollers, whereinthe at least one guide comprises a sliding member, or one or a pluralityof rollers, which abut against an outer surface of the workpiece (14,16).
 15. The device for the production of an internally cooled valve (4)in accordance with claim 11, 12, 13, or 14, further comprising: at leastone load cell on the at lease one guide, together with individuallydriven forming rollers (42, 44), and a controller that controls therotational speed of the forming rollers (42, 44) such that the force onthe guides is minimised.
 16. The device for the production of aninternally cooled valve (4) in accordance with one of the claims 12 to15, characterised in that the axes of the rollers are arranged skewedrelative to one another at an angle of 1° to 12°, preferably of 2° to10°, and more preferably of 3° to 8°.
 17. The device for the productionof an internally cooled valve (4) in accordance with claim 16,characterised in that the axis of the workpiece (14, 16) and the axes ofthe forming rollers (42, 44) are in each case arranged skewed relativeto one another at an angle of 0.5° to 6°, preferably of 1° to 5°, andmore preferably of 1.5° to 4°.
 18. The device for the production of aninternally cooled valve (4) in accordance with one of the claims 16 or17, wherein at least one of the forming rollers (44) has a hyperboloidalouter surface.
 19. The device for the production of an internally cooledvalve (4) in accordance with one of the claims 12 to 18, wherein atleast one of the forming rollers (42, 44) has a surface structure, whichcauses a transport of the material of the workpiece in the axialdirection.
 20. The device for the production of an internally cooledvalve (4) in accordance with one of the claims 12 to 19, furthercomprising: an axial guide or a clamping chuck, so as to guide and/orhold the workpiece (14, 16) from the disk face.
 21. The device for theproduction of an internally cooled valve (4) in accordance with one ofthe claims 12 to 20, further comprising: an actuator, so as to move theworkpiece (14, 16) axially, from the base in the direction of the valvestem end (36).
 22. The device for the production of an internally cooledvalve (4) in accordance with one of the claims 12 to 21, furthercomprising: a drive, so as to rotate the workpiece (14, 16) during therolling process at a predetermined rotational speed.
 23. The device forthe production of an internally cooled valve (4) in accordance with oneof the claims 12 to 22, further comprising: a heating element, so as toheat the workpiece (14, 16) during the rolling process.
 24. Aninternally cooled valve (4) for internal combustion engines,characterised in that it has been reshaped from a workpiece (14, 16)using one of the methods of claims 1 to 10, or using a device accordingto any one of claims 12 to 23, wherein the workpiece (14, 16) comprisesa stem, wherein the workpiece (14, 16) also comprises a cylindricalhole, which extends from one end of the valve stem (36) in the axialdirection, wherein at least one stem has been reshaped by form rollingof the stem to a smaller diameter.
 25. An internally cooled valve (4)for internal combustion engines in accordance with claim 24,characterised in that prior to the form rolling process the workpiece(14, 16) comprises a diameter of at least that of the valve disk (6),and in that a valve head is produced with a concave fillet by means ofform rolling.
 26. An internally cooled valve (4) for internal combustionengines in accordance with claim 24 or 25, characterised in that theworkpiece (16) is cup-shaped, wherein the cup-shaped workpiece (16) hasa diameter at a base of the workpiece (16) that corresponds at least tothat of the valve disk (6), wherein the cylindrical hole is a blind hole(26), which extends from one end of the valve stem (36) in the directionof the base of the cup-shaped workpiece (16).
 27. An internally cooledvalve (4) for internal combustion engines in accordance with claim 26,characterised in that the workpiece (16) is cup-shaped, wherein thecup-shaped workpiece (16) has a larger diameter at a base of theworkpiece (16) than in the area of the cylindrical stem.
 28. Aninternally cooled valve (4) for internal combustion engines inaccordance with one of the claims 24 to 27, characterised in that afterthe reshaping process the cylindrical hole (26, 28) forms a cavity (10)that extends within the valve stem (8) and the valve disk (6), whichcavity is partially filled with sodium (12) and sealed.
 29. Aninternally cooled valve (4) for internal combustion engines inaccordance with one of the claims 24 to 28, characterised in that priorto the rolling process the workpiece (14, 16) has a non-cylindrical stemwith an outer contour (70) and with a cylindrical hole (26, 28), whereinas a result of the reshaping of the valve stem end (36) by form rollingthe valve has a cylindrical valve stem and a non-cylindrical hole withan inner contour (72).